That is True. I have asked this question several times and this error dates from 2005. Some site:... command shows billions of pages indexed and the site in question just have thousands, so weired site: command had this error since 2005.

I think one of the major errors is for websites developed dynamically under some automatic parameters like regional parameters with unique titles etc.

I remember having about 5000 pages on my domain once when the site parameter, pretty impressive considering I've only ever written about 400 posts on my blog, I thought :)